<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    const p1 = () => {
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          console.log('p1触发了');
          resolve('a')
        }, 1000)
      })
    }
    const p2 = () => {
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          console.log('p2触发了');
          resolve('b')
        }, 500)
      })
    }
    const p3 = () => {
      return new Promise((resolve, reject) => {
        setTimeout(() => {
          console.log('p3触发了');
          resolve('c')
        }, 1500)
      })
    }
    p1()
      .then((res) => {
        console.log('res', res); // a
        return p2()
      })
      .then((res) => {
        console.log('res', res); // b
        return p3()
      })
      .then((res) => {
        console.log('res', res); // c
      }).catch(err => {
        console.log(err);
      })
  </script>
</body>

</html>